STUDIES ON BIOSYNTHESIS OF BETA-LACTAM ANTIBIOTICS .1. STEREOSPECIFIC SYNTHESES OF (2RS,3S)-[4,4,4-H-2(3)]-VALINE, (2RS,3S)-[4-H-3]-VALINE, (2RS,3R)-[4-H-3]-VALINE, AND (2RS,3S)-[4-C-13]-VALINE - INCORPORATION OF (2RS,3S)-[4-C-13]-VALINE INTO PENICILLIN-V